Hello!
I'm trying to understand if this is a bug, or a not clearly documented
feature.
I have a simple model where one field should be calculated at save. eg.
class MyModel(models.Model):
a = models.CharField(max_length=255)
b = models.CharField(max_length=255, blank = True)
Now, if I create an instance in the admin and I try to save leaving `b`
empty (that's ok because it's blank=True) I get a ValueError:
Cannot assign None: "app.MyModel" does not allow null values.
Now, I would expect to be able to set `b` to my calculated value in one of
the following places, according to the documentation:
- overriding save() in the model class
- in the clean() method in the model class
- with a custom save_model() in the admin class
Instead, none of those locations are reached, and I get the ValueError from
django/db/models/fields/related.py in __set__
1.
return rel_obj
2.
3.
def __set__(self, instance, value):
4.
# If null=True, we can assign null here, but otherwise the value
needs
5.
# to be an instance of the related class.
6.
if value is None and self.field.null == False:
7.
raise ValueError('Cannot assign None: "%s.%s" does not allow
null values.' %
1.
(instance._meta.object_name,
self.field.name))
now, also checking the stack (and even debugging) it seems like this comes
earlier than save.
*My question: **Is this somehow expected, is this a bug/a regression?*
If it's expected, I'll find another workaround; if it's a bug, I can add a
ticket.
Thanks!
Stefano
Stacktrack
- /home/3h/django/django/contrib/admin/options.py in add_view
1.
if form.is_valid():
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/forms/forms.py in is_valid
1.
return self.is_bound and not bool(self.errors)
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/forms/forms.py in errors
1.
self.full_clean()
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/forms/forms.py in full_clean
1.
self._post_clean()
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/forms/models.py in _post_clean
1.
self.instance = construct_instance(self, self.instance,
opts.fields, opts.exclude)
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/forms/models.py in construct_instance
1.
f.save_form_data(instance, cleaned_data[f.name])
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/db/models/fields/__init__.py in save_form_data
1.
setattr(instance, self.name, data)
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
- /home/3h/django/django/db/models/fields/related.py in __set__
1.
(instance._meta.object_name,
self.field.name))
...
▶ Local vars <http://grigio.vm:8000/admin/ipr/ipr/add/#>
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